To prevent reflection of a surrounding scenery in a display surface of a liquid crystal display, an organic electroluminescent (EL) display, or others, the display surface is usually kept away from regular reflection by coating or applying a mixture of a fine particle and a binder resin or curable resin on a support to form a finely (or minutely) uneven structure (minute recesses and projections) on the surface, and has anti-glareness. For a high definition display having a fine pixel size, unfortunately, a conventionally used surface-uneven size brings about debasement of an image, such as sparkling of transmitted images (or pictures) or blur of characters. Specifically, for the high definition display apparatus, the degree of the conventionally used surface-uneven size is close to that of the pixel size in the high definition display, and sparkling is generated due to a lens effect caused by the surface unevenness. Moreover, since the centroid position of the fine particles is unable to control in the inside and surface structures of a coat layer, the transmitted scattered-light distribution shows the Gaussian distribution with a central focus on a rectilinear transmitted light. In a conventional fine particle size, accordingly, the scatteration on the periphery of the rectilinear transmitted light increases; this makes the pixel border vague or unclear and thus induces blur (or clouding) of characters. Further, the intensity distribution of the transmitted scattered-light depends on the size of a fine particle added; a smaller fine particle decreases scattering on the periphery of the rectilinear transmitted light and reduces sparkling, and a larger fine particle increases scattering on the periphery of the rectilinear transmitted light and causes sparkling.
In order to solve these problems, the control of the uneven surface structure (or the surface structure having recesses and projections) is being attempted by reducing the size of a fine particle to be added or by using a fine particle having a narrow and sharp particle size distribution. In these manners, however, the control of the centroid position of the fine particles is necessary for preventing sparkling or blurred characters. Moreover, a smaller uneven surface structure makes it difficult to attain both adequate anti-glareness and prevention of sparkling or blurred characters, and such a manner is unfavorable in view of cost performance.
Japanese Patent Application Laid-Open Publication No. 2001-215307 (JP-2001-215307A; see Claims) discloses an anti-glare layer containing a transparent fine particle having an average particle size of not larger than 15 μm in a coat layer whose thickness is not less than twice of the average particle size, wherein the anti-glare layer has a surface having a finely uneven structure through uneven distribution of the transparent fine particles in one side being in contact with air of the coat layer. This document also discloses an optical member comprising a polarizing plate or an elliptically polarizing plate, at least one side of the polarizing plate or the elliptically polarizing plate having the anti-glare layer.
Unfortunately, for this anti-glare layer, since the intensity distribution of the transmitted scattered-light is controlled by changing the particle size, sparkling or blurred characters (blur of characters) on a display surface cannot be prevented effectively.
Japanese Patent Application Laid-Open Publication No. 2011-13238 (JP-2011-13238A; see Claims, paragraphs [0012] and [0035]) discloses, as an anti-glare film having an uneven surface structure that provides anti-glareness and high contrast, an anti-glare film comprising a translucent support and an anti-glare layer laminated thereon, wherein the anti-glare layer has a bicontinuous structure having a net-like (or network-like) pattern with a size of each net-like pattern (or cell) of 10 to 150 μm in a horizontal direction and at least contains a first phase and a second phase. According to this document, the bicontinuous structure is formed by aggregating an inorganic component in the anti-glare layer in film formation. The document defines the term “bicontinuous structure” as a structure having a peak (projection or protruded portion) with a smaller and gentler slope (inclination) in an uneven surface structure compared with a surface structure of a conventional anti-glare layer.
The bicontinuous structure described in the document is formed by convection with aggregation of the inorganic component. Unfortunately, since it is difficult to regulate the convection precisely, the resulting bicontinuous structure lacks uniform size of each net-like pattern and uniform thickness (width) of each net (or cell wall). Thus a finely uneven structure by which sparkling is reduced and a coarsely uneven structure by which sparkling is increased coexist in the anti-glare layer; it is essentially impossible to achieve both sparkling reduction and anti-glareness. Further, an uneven structure having a small size of each net-like pattern can reduce sparkling, while the anti-glare layer fails to show sufficient anti-glareness. In contrast, an uneven structure having a large size of each net-like pattern cannot reduce sparkling because the degree of the surface-uneven size is close to that of the pixel size.
Meanwhile, it is also known that an uneven structure is formed on a surface by spinodal decomposition of resin components incompatible with each other. Japanese Patent No. 4377578 (JP-4377578B; see claim 1, paragraphs [0058], [0059], [0071] and [0083], and Examples) discloses an anti-glare film comprising an anti-glare layer, wherein the anti-glare layer has an uneven surface structure, isotropically transmits and scatters an incident light, contains at least one polymer and at least one curable resin-precursor, and has a phase-separation structure. This document discloses that, for a process of producing a sheet by evaporating a solvent from a uniform solution containing at least one polymer and at least one curable resin-precursor in the solvent, a phase-separated structure having a regularity in distance between phases and an uneven surface structure corresponding to the phase structure can be formed by spinodal decomposition under appropriate conditions and then curing of the precursor; and discloses that a high definition display (specifically, a liquid crystal display having a resolution of 150 ppi) equipped with the anti-glare layer having the regular phase-separation structure can effectively prevent (or subdue) sparkling of transmitted images and blur of characters. In particular, this document states that the bicontinuous structure is formed along with the progress of the phase separation, and further proceeding of the phase separation makes a droplet phase structure, that a droplet phase structure having at least an island domain is favorable in view of forming the uneven surface structure and of improving the hardness of the surface, and that the island domain can form an uneven surface structure on the anti-glare layer after drying. This document also discloses that the drying temperature for inducing the phase separation by spinodal decomposition may be a temperature lower than the boiling point of the solvent (for example, may be selected from the range of about 30 to 200° C.) and is preferably 40 to 80° C.; in Examples, the drying temperature is 60° C. or 80° C.
Japanese Patent Application Laid-Open Publication No. 2008-225195 (JP-2008-225195A; see Claims, paragraphs [0068], [0069], [0074] and [0075], and Examples) discloses an anti-glare film comprising a cured product of a (meth)acrylic resin having a weight-average molecular weight of 30000 to 1000000, a (meth)acrylic resin having a weight-average molecular weight of 1000 to 100000 and a polymerizable group, and a polyfunctional (meth)acrylate, the anti-glare film having a ridge with an average width of 0.1 to 30 μm formed dispersively in a random direction on a surface thereof, wherein the total ridge area is not more than 50% of a whole surface area of the anti-glare film. This document also discloses that a droplet phase structure having at least an island domain is favorable and that the island domain can form an uneven surface structure on the anti-glare film after drying. Further, the document states that, in order to induce convection and phase separation, a coating composition is preferably allowed to stand for a predetermined time at an ambient temperature or room temperature and then dried at a temperature lower than a boiling point of a solvent (for example, at a temperature of about 30 to 200° C., particularly preferably about 40 to 80° C.); in Examples of the document, a coating composition is allowed to stand for 10 seconds at a room temperature and then dried in an explosion-proof oven at 60° C. or 70° C. at a wind speed of 3 m/minute.
Unfortunately, these anti-glare films described in JP-4377578B and JP-2008-225195A cannot reduce sparkling while maintaining anti-glareness when disposed on a high definition display having a resolution of higher than 150 ppi (for example, a liquid crystal display or organic EL display having a resolution of not lower than 200 ppi). In particular, generally, a larger distance between a display surface and an anti-glare layer tends to promote easier generation of sparkling. A protective film for a display [a film to be attached to a surface of a display by a purchaser or a user] has an adhesive layer, which extends the distance between the display surface and the anti-glare layer; it is difficult to prevent sparkling. In addition, among high definition displays, an organic EL panel, having a high luminescence intensity of pixel, easily shows sparkling and has a difficulty in achieving both anti-glareness and prevention of blurred characters. These anti-glare films described in JP-4377578B and JP-2008-225195A cannot achieve well-balanced combination of both characteristics.